Britain's Northern Ireland Secretary Theresa Villiers said on Thursday she had resigned from the government after declining a new post offered to her by Prime Minister Theresa May.

May is in the process putting together her senior team after taking office on Wednesday.

"I regret to say that I have left the government. The new prime minister was kind enough to offer me a role but it was not one which I felt I could take on," Villiers, who campaigned for Brexit, said in a statement posted on Facebook.

"I am sad to bring to end my work in Northern Ireland but I believe that I leave the political situation there in a more stable position than it has been for many years ... I am confident that progress will continue to be made to embed peace, stability and prosperity there."